It is known that MDI prepolymers are useful in preparing cast polyurethane elastomers and that the chain extenders commonly employed with them are polyhydroxyalkanes, such as 1,4-butanediol. However, there are disadvantages to the MDI prepolymer/polyhydroxyalkane systems, e.g., their being so sensitive to stoichiometry that the components have to be used in almost exactly stoichiometric amounts, their sensitivity to processing temperatures, their inability to tolerate more than a very low moisture content, their requirement for long mold times, and the poor green strength of objects molded from them. It would be desirable to have an MDI prepolymer/chain extender system which does not suffer those disadvantages.
U.S. Pat. Nos. 4,296,212 (Ewen et al.), 4,523,004 (Lin et al.), 4,530,941 (Turner et al.), and 4,659,747 (Alberino et al.) teach diol/diamine mixtures which can be used as chain extenders in RIM processes. U.S. Pat. No. 4,146,688 (Schwindt et al.) teaches the optional use of a minor amount of a diol or triol with certain thio group-containing aromatic diamine chain extenders in the preparation of polyurethanes. U.S. Pat. No. 4,595,742 (Nalepa et al.) discloses poly(alkylthio)aromatic diamine chain extenders having at least two alkylthio substituents on the same ring as at least one of the amino substituents.